vignettes monthly climate

[VeruGHub]

This is the branch with the new version: https://github.com/VeruGHub/easyclimate/tree/monthlydata. Syncronize it and Build > Install to have this version in your computer.

For the updates of the vignettes:

• Add here an example for montly data similar to the daily data
• Here I started to add an example with montly data. Can you finish it?
• Maybe here you can extract the montly values based in the same matrix of coordinates and add the average values to the previous plot.
• Tmax should be Tmin (https://github.com/VeruGHub/easyclimate/blob/053731c24fd195b99c7d78af9a6c1febe491a578/vignettes/polygons-raster.Rmd#L85)
• I would add here an example of how you get a raster of montly values. With get_montly_data you get two layers per variable: the values and the coverage (NAs in the data to calculate the montly average values), so you would need to manage this to make the plot.
• Remove all montly aggregations here, although I would keep an example about aggregating by year

This is all I have seen so far. Any other improvement on the vignettes or plotting is welcome too :) Thanks